The invention relates to a carrier for a guide vane and a heat protection shield for a guide vane in a thermal turbo machine, such as, for example, a turbine part or compressor of a gas turbine, in order to achieve minimal radial vane play.
In thermal turbo machines, radial vane clearance(a) exists between the rotating vanes and stationary housing, as well as between guide vanes and rotor. This vane clearance is determined during operation by mechanical and thermal movement of the various machine parts. In the process, different vane clearance are created during the various operating conditions, such as, for example, during start-up and shut-down, constant performance operation, and load changes, because the vanes, housing and rotor expand and contract differently. If the vane clearance is made sufficiently large to prevent a rubbing of the machine parts in all operating situations, this will provide an undesired, large vane clearance in certain operating conditions that will cause a reduction in the performance of the gas turbine or pumping limit of a compressor.
Previous attempts to decrease vane clearance and thereby increase the performance of the turbo machine always included efforts to maintain the level of production costs and life span of the machine. In order to limit the expansion of the stationary housing, this included, for example, the forced cooling of the stationary housing or materials with low coefficients of expansion.
DE 1 057 827 describes a vane wheel rim with a groove facing the rotating vane tips. Into the groove are inserted heat-resistant and abradable sealing elements consisting of a thermically designed expansion body whose mass distribution, clamping and positioning is such that the vane clearance is maintained approximately constant during temperature changes. This is achieved, for example, by a curvature of the sealing element in an axial direction, whereby the curvature changes during cooling or heating in such a way that a small gap is maintained. On the other hand, a small gap is achieved in that the abradable surfaces rest against the guide vane tips during the installation of the sealing elements and abradable off when the machine starts up. The abradable also achieves the smallest gap possible and prevents a breaking of the vane tips.
DE 43 09 199 describes a device for attaching heat shield segments and guide vanes in turbines with an axial flow. Here, the heat shield segments are attached to a massive stator ring that is inserted into recesses in the exterior housing of the turbine. The guide vanes are thereby attached, separately from the heat shield segments, directly to the exterior housing. The massive stator rings are sized relatively small so that their temperature and the vane play between the massive stator ring and vane tips can be better controlled. The temperature of the massive stator ring can also be controlled with cooling by air or fluids or by electrically heating, so that the vane plays can be controlled.
U.S. Pat. No. 5,927,942 and U.S. Pat. No. 5,380,150 describe a heat shield segment in a gas turbine that is attached radially opposite from the rotating vane tips on the stationary housing. Each heat shield segment consists of a substrate with a abradable layer. It is connected radially and axially on both sides as well as in the center of the heat shield segment by means of rails that have a hook-shaped cross-section to a carrier unit on the housing of a turbine machine, whereby the hooks are provided in recesses in the carrier unit. A segmented, spring-loaded band furthermore extends between the hooks on both sides of the heat shield segment. The band permits, in particular, a springing attachment of the heat shield segment at the carrier unit, thus absorbing any instances of thermal expansion and deformation of the heat shield segment and carrier unit. This attachment enables a radial as well as axial movement of the heat shield segment, whereby the rail in the center of the heat shield segment prevents a radial inward movement. The segmented band furthermore ensures a seal that prevents the coolant from flowing out of the space between the heat shield segment and the segmented band. And finally, the heat shield segment has a abradable layer for minimizing the rotating vane play.
The disadvantage of the heat shield segment or heat protection shield according to the described state of the art is, on the one hand, the abradable layers. In most machines, for example in gas turbines, the worn-off material remains inside the machine housing in the form of particles and may damage surfaces and obstruct cooling channels. The vane play created in this way does not necessarily have the optimally small size. When the turbo machine is started, the rotor first expands, while the housing of the turbo machine expands more slowly. If the abradable layers are worn off during the start-up, the vane play is again increased by the expansion of the housing and is not necessarily optimal during steady state operation.
In addition, heat shield segments of this type and their individual attachment on the housing of the turbo machine only regulate the rotating vane play, while the guide vane play must be adjusted with a separate construction.
This results in the objective of the invention, which is to create a carrier for guide vanes and a heat shield segment arranged radially opposite from the rotor vane tips for a thermal turbo machine, where said carrier and heat shield segment achieve a minimal, radial play between the tips of the . . . vanes and the rotor and between the tips of the guide vanes and the heat shield segment, whereby this minimal vane play should be maintained in as many operating conditions as possible. In particular, damage caused by material from abradable layers should be avoided. The production costs and life span of the components hereby should be at least maintained at the current or reduced level. The seal between the heat shield segment and housing also should be improved.
A thermal turbo machine with a rotor, rotor vanes, a stationary housing, and guide vanes is provided with a guide vane carrier that is attached to the housing of the turbo machine. The guide vane carrier is provided with a guide vane platform, to which are attached one or more guide vane airfoils. Heat shield segments are arranged radially opposite from the tips of the rotor vanes. According to the invention, an entire, axially adjoining heat shield segment or a part of two axially adjoining heat shield segments are part of the guide vane platform. Also, at least two braces extend at an angle to the guide vane platform, in part radially outward, towards a band. The braces hereby each extend in different directions relative to each other, in the manner of open scissors, from the guide vane platform towards the band. The radially outer ends of the braces are connected by the band, whereby the band is attached to the stationary housing. Furthermore, the guide vane platforms as well as the braces are made, in particular, from a first material with a high coefficient of expansion, whereby the band consists of a second material with a coefficient of expansion that is lower in comparison to the first material.
By integrating guide vane platform and heat shield segment, both the radial play between the guide vane tip and rotor, as well as the one between the rotating vane tip and the heat shield segment are simultaneously determined by a single construction. As a result of material choice for the band on the one hand and for the braces and integrated guide vane platform on the other hand, the guide vane carrier with the heat shield segment exhibits a thermal behavior that results in minimal vane play during the various operating conditions of the turbo machine. Since the coefficient of expansion of the band is lower than that of the material of the braces and guide vane platform, the band expands less quickly than the braces. During the warming of the machine, the angled arrangement of the braces causes a scissors-like movement, so that the guide vane platform moves radially inward along with the heat shield segment. After the machine start-up has completed and during the steady state operation, this results in minimum vane play, and thus an improved efficiency of the turbine or compressor. During the machine shut-down, the expansion of the band and braces again changes at different rates so that the braces move similar to a movement during the opening of scissors, and the guide vane and heat shield segment move away from the rotor and prevent a brushing against the vane tips.
Compared to turbo machines according to the state of the art, the guide vane carrier with heat shield segment according to the invention achieves reduced vane play without using abradable layers, thus preventing damage due to worn-off material.
The integration of guide vane platform and heat shield segment furthermore eliminates a sealing point in each guide vane platform, which in the case of a two-part construction for heat shield segment and guide vane platform would be created between these two parts. In the turbo machine according to the invention, the number of sealing points is also greatly reduced, which again benefits performance.
The guide vane carrier with integrated heat shield segment according to the invention furthermore has the advantage of a more stable construction. Because of the lower number of components required, a simplified suspension on the stationary housing that requires less space is also possible. This also results in reduced costs.
According to the invention, the heat shield segment is part of the guide vane platform. The guide vane platform is hereby constructed as a single component with the heat shield segment, or, in a second case, the guide vane platform is constructed as a single component together with a carrier for the heat shield segment. In the latter case, the heat shield segment is attached to a carrier. In the embodiments of the invention described below, the guide vane platform integrated with the heat shield segment in each case refers to both of these cases.
In a first embodiment, each of three braces extend from the guide vane platform integrated with the heat shield segment towards the band, whereby the center brace of the three braces extends at a first angle towards the band, and the two exterior braces extend parallel to each other, at an angle, in the opposite direction to the center brace towards the band, so that the bands form a V-or X-shaped arrangement.
In a second embodiment, two braces extend from the guide vane platform towards the band, whereby each of these are arranged at an angle to the platform, so as to form a scissors-like X-shaped or V-shaped arrangement.
In a variation of these two embodiments, the braces extend from the guide vane platform in a scissors-like arrangement, by leading at an angle from the guide vane platform in part axially, in part radially outward towards the band. The xe2x80x9copen scissorsxe2x80x9d therefore are located in a plane parallel to the rotor axis or in a plane leading through the rotor axis.
In a variation, the braces and the band are constructed continuously in circumferential direction over the length of the guide vane platform.
In order to thermally stress relieve the guide vane carrier, the braces in another variation are constructed with arc-shaped cut-outs. For further thermal relief, the braces in a preferred variation are arranged together with the band arranged above them in the circumferential direction on the guide vane platform in several individual sections.
In another variation, each of the braces extends from the guide vane platform at an angle in part in circumferential direction, in part radially outward in a scissors-like arrangement towards the band. The xe2x80x9copen scissorsxe2x80x9d thus are in a plane vertical to the rotor axis.
In another variation, the joint between axially adjoining guide vane platforms with integrated heat shield segments is arranged according to the pressure distribution in the area of the rotating vane tip in such a way that a leakage flow through the joint is minimized.
The guide vane carrier with its integrated heat shield segment is in each case integrated in one or more recesses in the stationary housing of the turbo machine.
To further reduce leakages at the joints between integrated guide vane platforms, the guide vane platforms with the integrated heat shield segments of one guide vane row are arranged offset in relation to the integrated guide vane platforms of an adjoining guide vane row. This prevents the joints between two circumferentially adjoining guide vane platforms with joints from coinciding with the joints between two consecutive, integrated guide vane platforms of the next guide vane row. This creates a sort of labyrinth for the leakage flow, and the leakage flow is therefore reduced.
The leakage points in circumferential and axial direction are hereby further sealed with sealing elements of various types.
Finally, the space bordered by the guide vane platform with heat shield segment, the braces, and the band is in each case filled with air or a filler.